The present invention relates to automatic flow control valves and, in particular, it concerns a control valve with integrated dual actuators in which both of the actuators are deployed in a single, common control chamber.
Automatic control valves are known to utilize piston type actuators, or diaphragm type actuators having either a flat or rolling flexible diaphragm, as the drive mechanism for displacing the valve plug. The sliding piston seals or the flat or rolling diaphragms used are subject to ware and eventual failure due to movement and aging. Failure causes pressure loss from the control chamber, which usually causes the control valve itself to fail to the open position, that is, the main valve member moves to the fully raised position, which causes flow through the valve to increase, with consequent problems arising upstream or downstream depending on the application of the valve. Because the sliding seals or diaphragm are contained within the valve itself and are not visible from the outside, inspection of the seals or diaphragm without dismantling the valve is usually impossible, and thus there is a tendency to replace the seals or diaphragm prematurely rather than risk failure in normal use. Also, the control systems used to control the valves can fail, for example, due to blockage of a conduit with dirt, or failure of the pilot control valve to control properly, and thus, in very critical areas preventative maintenance costs can be considerable.
Some valves are designed to fail to the closed position and are termed “fail-safe” valves. While the failure of these valves can prevent damage in some applications, when they fail there is a complete cessation of flow through the valve, which in some applications can create other dangerous situations. Other valves use a parallel duplicate or redundant system in which both systems have some duplicating components which are operative simultaneously, and both are subject to wear, usually at the same rate, and thus are likely to fail at approximately similar moments in time.
In an attempt to provide a single valve that can maintain “normal” operation after failure of the primary actuator, U.S. Pat. No. 5,348,036, assigned to Singer Valve Inc., discloses a valve having two separate control chambers, each containing a separate actuator configured to interact with a common valve plug. The primary actuator controls displacement of the valve plug during normal operation while the secondary actuator is deployed in a fully open stand-by position. Upon failure of the primary actuator, the secondary actuator is activated so as to continue normal valve function. Essentially, this is an integration of two completely separate actuating systems configured to act upon a common valve plug (see FIG. 1). In fact, the embodiment currently marketed by Singer Valve Inc. does indeed resemble two actuator housings stacked one on the other (see FIG. 2).
Although the Singer valves are more compact and economical than the parallel duplicate or redundant systems, they are still much larger than regular single actuator valves. In addition, maintenance of the Singer valves requires accessing two separate control chambers.
There is therefore a need for a control valve with integrated dual actuators in which both of the actuators are deployed in a single, common control chamber. It would be of benefit if the outer dimensions of the valve were the same as or similar to the dimensions of a valve having a single actuator.